The invention relates generally to rolls for treating webs of material and, more particularly, to an improved hydrostatically supported roll having a rotatable hollow cylinder, a crosshead extending lengthwise therethrough and supporting elements disposed in the clearance space between the cylinder and crosshead.
In DE-PS 2432467, a flexure-controllable roll is disclosed having a rotatable hollow cylinder forming a working roll circumference and a stationary crosshead extending lengthwise through the hollow cylinder to form a surrounding clearance space with the inner circumference of the hollow cylinder. At least one hydrostatic supporting element is guided in a cylinder bore in the crosshead. Choke bores lead from the cylinder chamber underneath the supporting element into supply pockets formed in the contact surface of the supporting element. The contact surface of the supporting element abuts the inner circumference of the hollow cylinder. A threaded member is provided in the base of the cylinder chamber and is adjustable in the axial direction of the cylinder chamber. The threaded member has an internal cylinder bore within which a small piston is slidably received. The small piston is connected to the supporting element by means of piston rod-like member such that when the supporting element moves into its cylinder bore in the crosshead, the small piston, in turn, is pushed into its cylinder bore. The cylinder chamber of the small piston is connected with the cylinder chamber under the supporting element by a conduit, which has a throttle valve for adjusting the cross sectional area of the conduit and, hence, the flow therethrough. In this manner, the small piston acts like a damping element because as the small piston moves with the supporting element hydraulic fluid must be either displaced from or drawn into its cylinder chamber depending upon the direction of movement. The force that the small piston exerts on the supporting element is directed only against one side of the supporting element for forcing the supporting element against the inner circumference of the hollow cylinder. Hence, the ability of the small piston to control the flexure of the roll accordingly is limited. Furthermore, the force exerted by the small piston is derived from the pressure in the cylinder chamber of the supporting element.